A scanning-type distance measurement device adopts at least one of the time of flight (TOF) system or the amplitude modulation (AM) system, and is used in a visual sensor of a robot or an automatic guided vehicle, an open/close sensor of a door, a monitor sensor for detecting whether or not there is an invader into a to-be-monitored region, a safety sensor for detecting a person or an object approaching a dangerous machine so as to safely stop the machine, or the like.
As disclosed in Patent Document 1, the TOF system includes calculating a distance D from a scanning-type distance measurement device to an object located in a to-be-monitored region in accordance with a detection time difference Δt between pulse-shaped measurement light emitted to the to-be-monitored region and reflected light from the object with respect to the measurement light. The distance D is calculated in accordance with the following numerical expression. In this equation, C denotes light speed.D=Δt·C/2
As disclosed in Patent Document 2, the AM system includes calculating a distance D from a scanning-type distance measurement device to an object located in a to-be-monitored region in accordance with a phase difference Δφ between measurement light that is modulated in amplitude and emitted to the to-be-monitored region and reflected light from the object with respect to the measurement light. The distance D is calculated in accordance with the following numerical expression. In this equation, C denotes light speed and f denotes a modulation frequency.D=Δφ·C/(4π·f)
There is also proposed a scanning-type distance measurement device of the burst modulation system that includes both of the TOF system and the AM system. According to the burst modulation system, measurement light modulated in amplitude is emitted into a pulse shape, and a distance equal to or longer than one wavelength of the amplitude modulated light is calculated in accordance with the TOF system whereas a distance shorter than one wavelength of the amplitude modulated light is calculated in accordance with the AM system.
In any of these cases, a signal processing device of a scanning-type distance measurement device includes a distance calculation unit for calculating a distance from the scanning-type distance measurement device to an object located in a to-be-monitored region at each predetermined scan angle in accordance with a predetermined correlation relationship between measurement light and reflected light, more specifically, a correlation relationship between delay time or a phase difference therebetween and the distance.
Patent Document 3 discloses a scanning-type distance measurement device that includes an object detection means including a reception signal integration means for integrating reception signals corresponding to reflected light in each of a predetermined number of regions obtained by dividing a scan range to be scanned with use of measurement light and generating region measurement data, a region measurement data storage memory for storing the region measurement data for each of the regions, a chronological process means for chronologically filtering the region measurement data read out of the region measurement data storage memory, and an object detector for detecting an object in accordance with, in the region measurement data chronologically filtered by the chronological process means, data that has a first peak value at a current scan not being decreased by a predetermined constant or greater value from a second peak value at a last scan measurement in the same region, and excluding, from object detection targets, data that has the first peak value being decreased by the predetermined constant or greater value from the second peak value.